Coating solution and method for preparing the coating solution, method for forming insulating films for semiconductor devices, and method for evaluating the coating solution

ABSTRACT

A coating solution for forming an insulating film used in production of semiconductor devices includes siloxanes represented by a general formula: 
     
          SiR.sub.3 O.sub.1/2 !.sub.k  SiR.sub.2 O.sub.2/2 !.sub.l  SiRO.sub.3/2 
    
      ! m   SiO 4/2  ! n   
     where each of k, l, m and n is an integer, R may be the same or different and represents at least one organic group, and a ratio of (3k+2l+m) to (k+l+m+n) is between about 0.8 and about 1.3. The present invention further relates to a method for preparing the coating solution, and a method for forming the insulating film using the coating solution, including the steps of coating the coating solution on a surface of a substrate of the semiconductor device to form a coated film, fluidizing the coated film at a temperature between about 150° C. to about 300° C. to planarize the surface of the substrate, and curing the fluidized coated film to form the insulating film. The present invention permits the formation of the insulating film with excellent properties such as an ability of fill up fine groves and to planarize the surface of the substrate, and a small shrinkage factor. The method for evaluating the coating solution using  29  Si-NMR technique is also described.

TECHNICAL FIELD

The present invention relates to a method for evaluating siloxanes usedfor forming an insulating film which comprises determining the rates ofstructural units of siloxanes including, in particular, organicsubstituents directly bonded to Si atoms as a part of the structurethereof, present in a coating solution for forming an insulating film,i.e., a solution containing siloxanes which are used as precursors forforming an insulating film to level the surface of a substrate on whichuneven portions are formed and to electrically insulate the substrate,in particular, an interlayer insulating film for leveling distributingwire structures of electronic devices such as an LSI multilevelinterconnection structure and for insulating the multilevelinterconnection structure, and evaluating the siloxanes on the basis ofthe rates thus determined; a coating solution for forming an insulatingfilm, which comprises siloxanes and is used for producing asemiconductor device and a method for preparing the coating solution;and a method for forming an insulating film for semiconductor devicesand a method for producing a semiconductor device using the insulatingfilm-forming method.

BACKGROUND ART

Heretofore, the integration density of the semiconductor device has beenincreased, more finer and highly multilayered distributing wires forelements have correspondingly been required and, in turn, the stepsformed between these distributing wires have increasingly been high. Forthis reason, the ability of an insulating material to fill up the gapformed between distributing wires and the surface flatness of an elementafter forming an insulating film have become serious problems. Withregard to the tolerance in the flatness, the depth of focus of a resistbecomes small for ensuring a desired resolution during thephotolithography process and there has been reported that the unevennessof the surface of, for instance, a line-and-space pattern of 0.7 μmshould be limited to the level of not less than 200 nm. A chip or wafermust satisfy the foregoing requirement throughout the entire areathereof and therefore, the complete leveling of the chip or waferthroughout the entire area thereof is required according to its literalsense.

To solve these problems, there has presently been known a method forfilling up steps on the surface of a substrate to thus level the surfacethrough the formation of an insulating film by the chemical vapordeposition method using ozon and tetraethoxysilane as starting materials(O₃ -TEOS AP-CVD), as disclosed in Japanese Un-Examined PatentPublication (hereinafter referred to as "J. P. KOKAI") No. Sho 61-77695.

The O₃ -TEOS APCVD technique is excellent in the step coverage and canensure excellent filling up properties, but the insulating film isformed in conformity with distributing wires and therefore, it isimpossible to level the surface of a substrate over a wide area thereof.Moreover, the O₃ -TEOS APCVD technique also suffers from a problem suchthat the rate of deposition observed on a wide flat portion differs fromthat observed on fine and dense distributing wire patterns andaccordingly, it is difficult to flatten the surface of a pattern whosedistributing wire density varies depending on the position.

In addition, there has also been known a method which comprises grindingthe surface of a thick deposited insulating film by the chemicalmechanical polishing (CMP) technique as disclosed in, for instance, L.B. Vines and S. K. Gupta, 1986 IEEE VLSI Multilevel InterconnectConference, p. 506, Santa Clara, Calif. (1986) or R. Chebi and S.Mittal, 1991 IEEE VLSI Multilevel Interconnect Conference, p. 61, SantaClara, Calif. (1991) or B. M. Somero, R. P. Chebi, E. U. Travis, H. B.Haver, and W. K. Morrow, 1992 IEEE VLSI Multilevel Interconnect Conf.,p. 72, Santa Clara, Calif. (1992). It has been said that the CMPtechnique permits almost ideal leveling of the surface over a wide areaif appropriately establishing the conditions for the CMP technique.

However, grooves present between distributing wires should separately befilled up prior to carrying out CMP. More specifically, the CMPtechnique must be used in combination with other methods such as the CVDtechnique to fill up such grooves. Moreover, it has been pointed outthat the CMP technique per se suffers from various problems to be solvedsuch as a decrease in the throughput, formation of particles,metal/alkali contamination, uncertainty in the detection of the endpoint of polishing and an increase in the cost of equipment andaccordingly, this technique has not yet been widely used.

If taking notice of only the techniques for filling up the groovesbetween distributing wires, the high density plasma CVD technique inwhich a substrate is biased (Biased HPD CVD) has attracted interestrecently. S. Matsuo and M. Kiuchi, Jpn. J. Appl. Phys., 22, L210 (1983)or K. Machida and H. Oikawa, J. Vac. Sci. Technol., B4, 818 (1986).Thistechnique is a method comprising depositing an oxide film whileanisotropically sputter-etching the surface of a substrate with argonions, unlike the currently used CVD technique, and the technique makesuse of ECR or ICP which can ensure a high plasma ion density as a plasmasource.

The HDP technique for forming interlayer insulating films is consideredto be an almost satisfactory technique for filling up grooves, butprojections are formed on the entire surface of a distributing wirepattern due to insufficient sputter etching and therefore, the levelingof the surface should separately be carried out by, for instance, theCMP technique. Moreover, the problems such as particle-formation andreduction in throughput due to the low deposition rate have not yet beensolved.

On the other hand, there has widely been adopted, in the production ofsemiconductor devices, a method for relieving the unevenness of asubstrate by forming an insulating film according to the SPIN ON GLASS(SOG) method as disclosed in, for instance, OYO BUTSURI (AppliedPhysics), Vol. 57, No. 12 (1988). For instance, a hard film comprisingSiO₂ formed by the SOG method has generally been used as an interlayerinsulating film for LSI multilevel interconnections.

The term "SOG" means a technique comprising applying a solutioncontaining oligosilanols or oligosilicates to a substrate by aspincoater and then thermally hardening the coated solution to form ahard film of SiO₂, or an insulating film formed by the method, or acoating liquid for forming an insulating film. The SOG coating solutionmay run into narrow grooves formed between distributing wires and thefilm thus formed may correspondingly fill up the grooves andsimultaneously flow into wide and flat recesses. Therefore, the coatingsolution also permits leveling of the surface having relatively wide andhigh steps. The SOG process is performed at a low temperature on theorder of about 400° C. and therefore, it can be recommended to use thesolution for forming interlayer insulating films after the formation ofAl distributing wires which are apt to be easily damaged by heating.

There have conventionally been used, as materials for SOG, anoligosilicate called inorganic SOG represented by the general formula:Si(OR)_(n) (OH)_(4-n) and completely free of organic groups bonded to Siatoms. The inorganic SOG undergoes volume shrinkage at a rate of about20% during hardening with heating. Accordingly, the resulting film has apoor resistance to crack and the inorganic SOG can be coated in athickness ranging from only 200 to 300 nm by a single coating operation.An SOG film having a thickness at least equal to the height ofdistributing wires is required for relieving the steps formed bydistributing wires whose cross section has an aspect ratio greater thanabout 1, but such a thick SOG film cannot be formed because theinorganic SOG may cause cracking. In other words, the inorganic SOGcannot be used for leveling a stepped pattern having a high crosssectional aspect ratio.

To eliminate the foregoing drawbacks associated with the inorganic SOGand to improve the shrink properties, flatness, adhesion and resistanceto cracks of a film as well as the etch rate thereof, there has beeninvestigated and developed an oligosiloxane called organic SOG whichcomprises, in the chemical structure, organic substituents directlybonded to an Si atom, i.e., an organic Si and which is represented bythe general formula: R_(m) Si(OR)_(n) (OH)4-n-m. Methyl group is mainlyused as the organic substituent because of its thermal stability,gas-generating properties, resistance to plasma, yield value of theresulting film and flexibility thereof, but other kinds of substituentssuch as a phenyl group may sometimes be used as the organic substituent.The organic SOG is characterized in that the film thereof has a lowshrinkage factor during hardening with heating as compared with the filmof the inorganic SOG and therefore, the film has high resistance tocracks. In addition, the rate of etching the film with a CHF₃-containing etching gas is low and almost comparable to that of the CVDfilm. Therefore, the organic SOG permits the use of a leveling processby the equal velocity etch back method which comprises applying a thickorganic SOG layer on a CVD oxide film formed on a pattern, thenhardening the organic SOG layer and etching the hardened SOG layer witha CHF₃ -containing etching gas simultaneously with the CVD film.

However, the hardening of the SOG layer by heating is initiated at about100° C. and this is accompanied by the volume shrinkage of the SOGlayer. Thus, the surface which is once flatened by the application ofthe organic SOG ultimately has unevenness corresponding to the shape ofthe surface of a substrate and the flatness of the surface is notimproved so much.

Moreover, it has been believed that the range of the area on a substratewhich is under the influence of the leveling effect due to the flow ofthe coating solution is limited to local one and only on the order of 10μm and thus the thickness of the film on the recesses between widedistributing wires of not less than 10 μm is approximately identical tothat of the film on the projected portions, i.e., on the distributingwires. More specifically, the steps formed between resesses andprojected portions are not relieved at all from the visual field on theorder of not less than 10 μn. As has been discussed above, the thicknessof the film formed varies depending on the density of the wiring patternand therefore, the organic SOG is useless for leveling a wide areacomparable to those of chips and wafers.

Moreover, the organic SOG undergoes volume shrinkage on the order of atleast about 7% during hardening with heating and may crack due to thecontraction stress if a film thereof having a thickness of not less than500 nm is formed by coating, like the inorganic SOG.

The organic SOG film is inferior in the quality and liable to retain orabsorb water. For this reason, various troubles are liable to arise dueto the gas generated from the SOG film in the subsequent processes.Moreover, the organic SOG film suffers from various problems such thatthe apparent dielectric constant thereof increases due to the presenceof water, the delay increases due to the interline capacity and thus itis insufficient for use as an insulating film for high speedinterconnections.

There has been reported several kinds of SOG's which can eliminate theforegoing drawbacks associated with the organic SOG. One of them is aladder siloxane oligomer which can be represented by the followingstructural formula: ##STR1## In other words, a methyl group (or a phenylgroup) is bonded to each Si atom and the oligomer has a ladder-likeregular structure.

The ladder siloxane oligomer causes melt flow through heating like thecrystals because of high structural regularity, but suffers from fataldrawbacks such that it cannot form a thick film because of the highshrinkage factor and poor resistance to cracks and that it is lacking instructurally active hydroxyl groups (Si--OH), poorly adhered to thesubstrate and is liable to cause peeling.

As another measure, there has been known an inorganic SOG prepared fromhydrogensiloxane oligomer or perhydrosilazane oligomer. These novelSOG's have a structure free of organic groups directly bonded to Siatoms and are, instead, characterized by having hydrogen atoms directlybonded to Si atoms. Either of them can be used for forming a thick filmsince it undergoes expansion through absorption of oxygen present in theatmosphere in a furnace during hardening with heating after coating anddrying and accordingly has a low apparent shrinkage factor. However,they suffer from a problem such that the uneven shape of the substratesurface is traced on the films thereof due to the shrinkage duringapplication and drying thereof, like the organic SOG and therefore, theycannot be used for leveling the surface over a wide area. Furthermore,free hydroxyl groups remain in the film even after hardening withheating and this becomes a cause of gas-generation and a high dielectricconstant.

There has not yet been developed any material which can solve theproblems listed above.

On the other hand, the improvement of characteristic properties ofinsulating films for semiconductor devices, in particular, interlayerinsulating films for the LSI multilevel interconnection requires theanalysis of the siloxanes constituting the insulating films.

As methods for analyzing siloxanes included in a variety of materials,there have been known those comprising analyzing a sample as such orsiloxanes extracted with an appropriate organic solvent by, forinstance, infrared spectrophotometry, nuclear magnetic resonance (NMR)spectroscopy, inductive coupled plasma emission spectroscopic analysis(J. P. KOKAI No. Hei 4-40347). In addition, there has also been known amethod which comprises chemically decomposing siloxanes to formdecomposition products thereof and detecting and analyzing the products(Japanese Examined Patent Publication (hereinafter referred to as "J. P.KOKOKU" ) No. Sho 62-8146). However, the purpose of all of these methodsis to determine the total amount of Si present in a specific material.

Although several methods for analyzing siloxanes have been known as hasbeen discussed above, there has not yet been established anyindustrially effective method for determining the proportions of organicsubstituents present in the organic SOG and, in particular, anyindustrially useful method for accurately and simply analyzing andevaluating the organic SOG, i.e., siloxanes for forming insulating filmswhile correlating the results with the characteristic properties ofinsulating films for semiconductor devices, in particular, interlayerinsulating films for the LSI multilevel interconnection. Moreover, therehave been desired for the development of a coating solution for formingan insulating film which can sufficiently improve the characteristicproperties of insulating films for semiconductor devices, in particular,interlayer insulating films for the LSI multilevel interconnection and amethod for preparing the same as well as a method for forming aninsulating film for semiconductor devices.

DISCLOSURE OF THE INVENTION

The present invention has been developed for the solution of theforegoing problems associated with the conventional techniques andaccordingly, an object of the present invention is to provide a methodcomprising analyzing the rates of organic substituents present in anorganic SOG, and determining the rates of Si atoms bonded to differentnumbers of organic groups, i.e., structural units present in the organicSOG or siloxanes for forming an insulating film for semiconductordevices; and evaluating the siloxanes for forming insulating films onthe basis of the results obtained through the analysis, for the purposeof forming an insulating film, in particular, an interlayer insulatingfilm having excellent film characteristic properties.

Another object of the present invention is to provide a coating solutionfor forming an insulating film using siloxanes, which permits completelyfilling up fine grooves, formation of a film having a thicknesssufficient for eliminating steps on the substrate surface and uniform(and global) leveling of the entire pattern formed on the substrate andwhich permits the formation of an insulating film free of water, havinga low dielectric constant and favorable for a high speedinterconnection, i.e., an insulating film excellent in filmcharacteristic properties, in particular, an interlayer insulating filmfor semiconductor devices, as well as a method for preparing the coatingsolution, a method for forming an insulating film for semiconductordevices and a method for producing a semiconductor device using theinsulating film-forming method.

The inventors of this invention have conducted intensive studies oncharacteristic properties of siloxanes and interlayer insulating filmsfor LSI multilevel interconnections obtained using siloxanes, have foundout that the characteristic properties of the insulating film aregreatly influenced by the rates of organic substituents present in thesiloxanes or the rates of Si atoms carrying different numbers of organicgroups bonded thereto, i.e., the rates of structural units of thesiloxanes present in the organic SOG and that, as a result of intensivestudies, the organicity of SOG can be evaluated on the basis of theintegrated values of ²⁹ Si-NMR spectral signals and that an insulatingfilm having excellent film characteristic properties can be obtained bythe use of a coating solution of an organic SOG prepared while takinginto consideration the results of the foregoing evaluation, and thushave completed the present invention.

According to a first embodiment of the present invention, there isprovided a method for evaluating siloxanes for forming an insulatingfilm which comprises evaluating siloxanes which comprise Si atoms eachcarrying at least one organic substituent bonded thereto contained in acoating solution for forming an insulating film, characterized bydetermining the rates of three kinds of Si atoms each having the numberof the organic substituents bonded thereto ranging from 1 to 3 and therate of at least one of Si atoms free of the foregoing organicsubstituent to thus determine, for instance, the content of organicsubstituents on the basis of the foregoing proportions and evaluatingthe siloxanes for forming an insulating film, for instance, theorganicity thereof.

In this respect, the rates of the Si atoms carrying different numbers oforganic substituents bonded thereto are preferably determined throughthe use of the integrated values of ²⁹ Si-NMR spectral signals.

In addition, it is preferred that the siloxanes which comprise the Siatoms each carrying at least one organic substituent bonded thereto bethose for forming an interlayer insulating film for LSI multilevelinterconnections represented by the following Formula 1! and that theproportion of at least one of the following structural units (a), (b),(c) and (d) present in the siloxanes be determined by the integratedvalues of ²⁹ Si-NMR spectral signals. ##STR2##

In Formula 1a!, or equivalently SiR₃ O_(1/2) !_(k) SiR₂ O_(2/2) !_(l)SiRO_(3/2) !_(m) SiO_(4/2) !_(n), . . . 1b!k, l, m and n each representsan integer ranging from 0 to 1000, and at least one of k, l and m isgreater than zero; R may be the same or different and represents atleast one organic group selected from the group consisting of saturatedhydrocarbon groups, unsaturated hydrocarbon groups, and a phenyl group,provided that the phenyl group may be a substituted phenyl group; andthe oxygen atoms each is linked to either of Si, R and H. ##STR3##

In the foregoing structural units (a), (b), (c) and (d), R may be thesame or different and represents at least one organic group selectedfrom the group consisting of saturated hydrocarbon groups, unsaturatedhydrocarbon groups and phenyl group, provided that the phenyl group maybe a substituted phenyl group.

Moreover, the siloxanes comprising the Si atoms carrying at least onekind of the organic group are preferably siloxane oligomers. The degreeof polymerization of the siloxane oligomer represented by the number ofthe repeating structural units k+l+m+n! preferably ranges from 2 to 500.

According to a second embodiment of the present invention, there isprovided a coating solution for forming an insulating film, which is acoating solution for forming an insulating film used in the productionof semiconductor devices, wherein the solution comprises siloxanes whichcomprise Si atoms carrying at least one kind of organic substituentbonded thereto, which are represented by the following general Formula1a! and whose rate, X, represented by the following Formula 2!anddetermined by the integrated values of ²⁹ Si-NMR spectral signals,satisfies the relation defined by Formula 2!: ##STR4## In Formula 1a!,or equivalently SiR₃ O_(1/2) !_(k) SiR₂ O_(2/2) !_(l) SiRO_(3/2) !_(m)SiO_(4/2) !_(n), . . . 1b! k, l, m and n each represents an integerranging from 0 to 1000, and at least one of k, l and m is greater thanzero; R may be the same or different and represents at least one organicgroup selected from the group consisting of saturated hydrocarbongroups, unsaturated hydrocarbon groups, and a phenyl group, providedthat the phenyl group may be a substituted phenyl group; and the oxygenatoms each is linked to either of Si, R and H; ##EQU1## In Formula 2!,A₀ is the area of the Si signal ascribed to Si atoms free of Si--C bondand determined by the ²⁹ Si-NMR spectral analysis; A₁ is the area of theSi signal ascribed to Si atoms each having a single Si--C bond anddetermined by the ²⁹ Si-NMR spectral analysis; A₂ is the area of the Sisignal ascribed to Si atoms each having two Si--C bonds and determinedby the ²⁹ Si-NMR spectral analysis; and A₃ is the area of the Si signalascribed to Si atoms each having three Si--C bonds and determined by the²⁹ Si-NMR spectral analysis.

Moreover, the Si atom free of any Si--C bond, the Si atom having asingle Si--C bond, the Si atom having two Si--C bonds and the Si atomhaving three Si--C bonds are preferably Si atoms included in thefollowing structural units (c), (a), (b) and (d) respectively: ##STR5##

In the foregoing structural units (a), (b), (c) and (d), the substituentR may be the same or different and represents at least one organic groupselected from the group consisting of saturated hydrocarbon groups,unsaturated hydrocarbon groups and phenyl group, provided that thephenyl group may be a substituted phenyl group.

Moreover, the foregoing siloxanes are preferably siloxane oligomers. Thedegree of polymerization of the siloxane oligomer represented by thenumber of the repeating structural units: k+l+m+n! preferably rangesfrom 2 to 500.

Moreover, the present invention provides the foregoing coating solutionfor forming an insulating film wherein the foregoing siloxanes aredissolved in a solvent mainly comprising an organic compound having aboiling point of not less than 120° C. and not more than 200° C.

According to a third embodiment of the present invention, there isprovided a coating solution for forming an insulating film used in theproduction of semiconductor devices, wherein a methylsiloxane oligomerrepresented by the chemical formula: (CH₃)_(y) SiO₂₋(y/2) (in theformula, y is not less than 0.8 and not more than 1.3) and having aweight-average molecular weight of not less than 1500 and not more than6000 and a random structure is dissolved in a solvent mainly comprisingan organic compound having a boiling point of not less than 120° C. andnot more than 200° C.

In this regard, the solvent preferably has a coefficient of viscosity,as determined at 25° C., of not more than 2.0 cP and preferablycomprises at least one member selected from the group consisting ofethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether,propylene glycol monomethyl ether, ethylene glycol monoethyl etheracetate, diethylene glycol dimethyl ether, di-n-butyl ether, di-isobutylether, di-n-amyl ether, methyl n-amyl ketone, methyl isoamyl ketone,n-amyl acetate, isoamyl acetate and n-hexyl acetate.

According to a fourth embodiment of the present invention, there isprovided a method for preparing a coating solution for forming aninsulating film which makes use of a compound selected from the groupconsisting of tetraalkoxysilanes, methyltrialkoxysilanes anddimethyldialkoxysilanes or mixtures of at least two of them as astarting material, and which comprises the steps of blending thestarting materials in such a manner that the molar concentration ofSi--CH₃ in the resulting blend is not less than 80% and not more than130% on the basis of the molar concentration of Si present in the totalstarting materials, adding water to the blend in an amount of 2 to 4times the molar amount of the blend, heating the mixture at atemperature of not less than 30° C. and not more than 80° C. in thepresence of an organic carboxylic acid as a catalyst to thus polymerizethe mixture, diluting the polymerized product by addition of a solventmainly comprising an organic compound having a boiling point of not lessthan 120° C. and not more than 200° C. and then distilling the dilutedsolution under ordinary pressure or a reduced pressure to thus distilloff the water and the alcohol as by-products of the polymerizationreaction.

In this method, the tetraalkoxysilane is preferably tetramethoxysilaneand/or tetraethoxysilane; the methyltrialkoxysilane is preferablymethyltrimethoxysilane and/or methyltriethoxysilane and thedimethyldialkoxysilane is preferably dimethyldimethoxysilane and/ordimethyldiethoxysilane. Preferably, the foregoing organic carboxylicacid is at least one member selected from the group consisting of formicacid, acetic acid and succinic acid and the concentration thereof rangesfrom 1/1000 to 1/100 mole on the basis of the foregoing startingmaterial.

In the foregoing method for preparing a coating solution for forming aninsulating film, an alcoholic solvent is preferably added to thepolymerization system in an amount ranging from 0.2 to 3 times the molaramount of the starting material prior to the polymerization reaction,and the alcoholic solvent is preferably at least one member selectedfrom the group consisting of methanol, ethanol and dioxane.

Moreover, the foregoing solvent preferably has a coefficient ofviscosity, as determined at 25° C., of not more than 2.0 cP and thesolvent is preferably at least one member selected from the groupconsisting of ethylene glycol monoethyl ether, ethylene glycolmonoisopropyl ether, propylene glycol monomethyl ether, ethylene glycolmonoethyl ether acetate, diethylene glycol dimethyl ether, di-n-butylether, di-isobutyl ether, di-n-amyl ether, methyl n-amyl ketone, methylisoamyl ketone, n-amyl acetate, isoamyl acetate and n-hexyl acetate.

According to a fifth embodiment of the present invention, there isprovided a method for forming an insulating film for semiconductordevices which comprises the steps of applying the foregoing coatingsolution for forming an interlayer insulating film onto a distributingwire pattern formed on a silicon substrate and having step-likeunevenness on the surface of the pattern, then drying the coatedsolution, maintaining the dried coating solution at a temperature of notless than 150° C. and not more than 300° C. for not less than 30 secondsto thus fluidize it and then hardening it at a temperature of not lessthan 350° C. and not more than 450° C. in a nitrogen gas atmosphere toform an insulating film.

Further the present invention also provides a method for producing asemiconductor device which makes use of the foregoing method for formingan insulating film for semiconductor devices.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an ²⁹ Si-NMR spectrogram of the sample A (see Table 1) used inExample 1.

FIG. 2 is a graph showing the relation between the value X defined byFormula 2! in Example 2 and the shrinkage factor, the relativedielectric constant or the water absorption of an insulating film.

FIGS. 3A, 3B and 3C are schematic partially sectional views showing aprocess for forming a distributing wire pattern, a CVD oxidefilm-forming process and a process for forming an insulating film in themethod for producing an insulating film for semiconductor devicesaccording to the present invention, respectively.

FIG. 4 is a schematic cross sectional view showing a step formed on aninsulating film, for explaining the method for determining DOP as ameasure for the flatness as determined in Example 3.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will hereinafter be described in more detail.

The first embodiment of the present invention relates to an evaluationmethod which comprises the steps of determining the rate of at least oneSi atom carrying a different number of organic substituents bondedthereto, present in siloxanes which comprise Si atoms each carrying atleast one kind of organic substituent bonded thereto and which areincluded in an insulating film-forming coating solution used for formingan insulating film for semiconductor devices such as an interlayerinsulating film for LSI multilevel interconnections; determining, forinstance, the contents of the organic substituents present in thesiloxanes according to or on the basis of the rate of at least one Siatom determined above; and then evaluating the siloxanes, for instance,the organicity thereof on the basis of the contents of the organicsubstituents in the siloxanes. More specifically, the method comprisesdetermining the rate and the contents on the basis of the areas ofsignals obtained by the ²⁹ Si-NMR spectroscopy and evaluating theorganicity of the siloxanes.

The solution containing the siloxanes used in the present invention,i.e., the coating solution for forming an insulating film (hereinaftersimply referred to as "coating solution") may be any solution containingsiloxanes which is used as a precursor for forming an insulating filmfor semiconductors (hereinafter simply referred to as "insulating film")and which comprises siloxanes containing Si atoms each carrying at leastone kind of organic substituent or any solution in which such siloxanesare dissolved in an organic solvent and examples thereof include SOGsolutions for forming SOG films and organic SOG solutions. In thisrespect, the organic substituent may be at least one member selectedfrom the group consisting of saturated hydrocarbon groups, unsaturatedhydrocarbon groups and phenyl groups. Moreover, the number of organicgroups bonded to one Si atom may range from 1 to 3.

The siloxanes usable in the present invention can be represented by thefollowing Formula 1a!, but the way how to link these structural units isnot restricted to any specific one and they may be bonded in eitherlinear or branched form. Moreover, they may be used in any combination.##STR6## In Formula 1a!, or equivalently SiR₃ O_(1/2) !_(k) SiR₂ O_(2/2)!_(l) SiRO_(3/2) !_(m) SiO_(4/2) !_(n), . . . 1b! k, l, m and n eachrepresents an integer ranging from 0 to 1000, at least one of k, l and mis greater than zero; R may be the same or different and represents atleast one organic group selected from the group consisting of saturatedhydrocarbon groups, unsaturated hydrocarbon groups, and phenyl groups,provided that the phenyl group may be a substituted phenyl group; andthe oxygen atoms each is linked to either of Si, R and H.

Such siloxanes are preferably siloxane oligomers used for forminginsulating films and more preferably siloxane oligomers each having adegree of polymerization ranging from 2 to 500. More specifically, thenumber of the following repeating structural units (a) to (d): k+l+m+n!of the siloxane oligomer represented by the foregoing Formula 1!preferably ranges from 2 to 500. In this regard, if the degree ofpolymerization (number of repeating units) exceeds 500, the viscosity ofa coating solution (SOG solution) comprising siloxane and a solventbecomes extremely high, while if it is less than 2, the siloxane iseasily evaporated during the insulating film-forming step and in anycase, it is difficult to form an insulating film. ##STR7## In theforegoing structural units (a), (b), (c) and (d), the substituent R maybe the same or different and represents at least one organic groupselected from the group consisting of saturated hydrocarbon groups,unsaturated hydrocarbon groups and phenyl group, provided that thephenyl group may be a substituted phenyl group.

When evaluating siloxanes for forming insulating films, the method ofthe present invention comprises the step of determining the contents oforganic substituents of the siloxanes; or analyzing Si atoms carryingdifferent numbers of organic groups bonded thereto (Si atoms each havinga number of Si--C bond ranging from 0 to 4), i.e., at least one of theforegoing structural units (a) to (d) to determine the rate thereofpresent in the siloxanes. The methods for determining the contents oforganic substituents of siloxanes or for determining the rate of theforegoing structural units (a) to (d) present therein is not restrictedto any specific one, but the nuclear magnetic resonance (NMR)spectroscopy technique is preferably used. More preferably, such ratesof organic substituents are preferably obtained from the integratedvalues of ²⁹ Si-NMR spectral signals.

When carrying out the nuclear magnetic resonance (NMR) spectroscopicmethod, siloxanes such as SOG solution as a sample is first dissolved ina deutero solvent. The deutero solvent herein used is not restricted toany specific one insofar as it does not cause any separation ofcomponents of the SOG solution from the same through the addition of thesolvent and examples thereof usable herein include deutero chloroform,deutero acetone and deutero methanol. If the concentration of the sampleis too low, sufficient detection sensitivity is not expected, while ifit is too high, the proportion of the deutero solvent is reduced and thefrequency stability of the NMR spectrometer is impaired. Therefore, theconcentration of the sample preferably ranges from 10 to 90%.

It is preferred to use a sample tube of Teflon in the ²⁹ Si-NMRmeasurement. This is because if using the usual glass sample tube forNMR measurement, signals ascribed to ²⁹ Si originated from the silicateglass appear in the NMR spectrogram.

In the ²⁹ Si-NMR measurement performed in the present invention, it isdesirable that the decoupling of proton be not performed. This isbecause the nuclear Overhauser effect in the ²⁹ Si-NMR measurement isnegative and correspondingly, the intensity of ²⁹ Si-NMR signals maysometimes be attenuated depending on samples. Thus, the quantitativenessof the intensity of the signal integration can be ensured.

Moreover, the addition of a relaxation agent such astris(acetylacetonato)chromium (III) or tris(acetylacetonato)iron (III)is also preferred to reduce the measuring time.

Every signals in the ²⁹ Si-NMR spectrogram thus determined areidentified and the rates of the structural units (a), (b), (c) and (d)or/and the contents of Si atoms carrying organic groups bonded theretoare determined on the basis of the signal areas thus obtained. Thecontents of organic groups can be defined in several different waysdepending on the purposes and such different definitions may properly beused depending on the purposes or according to need. For instance, ifthe area of the Si signal ascribed to Si atoms free of Si--C bonds isdenoted by A₀, the area of the Si signal ascribed to Si atoms eachhaving a single Si--C bond is denoted by A₁, the area of the Si signalascribed to Si atoms each having two Si--C bonds is denoted by A and thearea of the Si signal ascribed to Si atoms each having three Si--C bondsis denoted by A₃, the measure (represented by X) of the organicity ofsiloxanes can be defined by, for instance, the following Formula 3! or4!: ##EQU2##

Formula 3! is an equation representing the ratio of the number oforganic substituents to the number of Si atoms present in the siloxaneand Formula 4! is an equation representing the ratio of the number oforganic Si atoms to the number of Si atoms present in the siloxane. Theequation for evaluating the organicity is not restricted to theforegoing Formulas 3! and 4! and can be represented by other definitionsdepending on the purposes of the analysis.

In addition, the 2nd to 5th embodiments of the present invention relateto novel coating solutions containing siloxanes, which are evaluatedaccording to the foregoing evaluation method, for forming an insulatingfilm for semiconductor devices such as an interlayer insulating film forLSI multilevel interconnections (hereinafter simply referred to as"insulating film") and methods for forming insulating films using thecoating solutions. The coating solution according to the 2nd embodimentand the method for forming an insulating film using the same willhereinafter be detailed.

The inventors have found out that there is a close relation between thechemical structure of siloxanes and the characteristic properties of theresulting SOG film.

More specifically, the inventors have found out that if using a coatingsolution containing siloxanes, preferably siloxane oligomers whoseproportion X represented by the following relation and determined on thebasis of the integrated values of ²⁹ Si-NMR spectral signals satisfiesthe following equation 2!, the resulting insulating film exhibitsexcellent characteristic properties: ##EQU3## In the foregoing Formula2!, A₀ is the area of the Si signal ascribed to Si atoms free of Si--Cbond and determined by the ²⁹ Si-NMR spectral analysis; A₁ is the areaof the Si signal ascribed to Si atoms each having a single Si--C bondand determined by the ²⁹ Si-NMR spectral analysis; A₂ is the area of theSi signal ascribed to Si atoms each having two Si--C bonds anddetermined by the ²⁹ Si-NMR spectral analysis; and A₃ is the area of theSi signal ascribed to Si atoms each having three Si--C bonds anddetermined by the ²⁹ Si-NMR spectral analysis.

The reason why an insulating film having excellent characteristicproperties is formed when using a coating solution containing siloxaneswhose proportion X defined by the foregoing Formula 2! is not less than80% is, for instance, as follows: (1) the water absorption of theresulting film is reduced and therefore, the amount of generated gasesand the dielectric constant thereof are restricted to low levels; (2)the resistance to cracks of the film is improved and accordingly, thecoating solution can be applied in the form of a thick layer; and (3)the dry etch rate is reduced and therefore, a wide etch back margin canbe ensured.

Then the coating solution for forming an insulating film according tothe third embodiment of the present invention will be explained below.

In the coating solution according to this embodiment, the measure forthe organicity of the siloxanes is evaluated on the basis of theforegoing Formula 3!.

According to the third embodiment of the present invention, there isprovided a coating solution characterized by dissolving a methylsiloxaneoligomer represented by the chemical formula: (CH₃)_(y) SiO₂₋(y/2) (inthe formula, y is not less than 0.8 and not more than 1.3) and having aweight-average molecular weight of not less than 1500 and not more than6000 and a random structure in a solvent mainly comprising an organiccompound having a boiling point of not less than 120° C. and not morethan 200° C. The coating solution is characterized in that the value yin the chemical formula is not less than 0.8 and not more than 1.3unlike the conventional organic SOG (wherein y ranges from 0.3 to 0.6)and that the siloxane oligomer has a random structure while theconventional organic SOG includes a ladder siloxane having a regularstructure.

The shrinkage of the methylsiloxane oligomer during hardening byheat-polymerization can be almost completely eliminated by limiting thevalue y in the chemical formula of the methylsiloxane oligomer to notless than 0.8. Therefore, the coating solution can be applied as a thicklayer and is advantageous for leveling the layer. The water absorptionof the methylsiloxane oligomer can be made almost zero and thedielectric constant thereof can be reduced to not more than 3.5, by theforegoing limitation. While if the value y is less than 0.8, theresulting film exhibits characteristic properties similar to thoseobserved for the usual organic SOG and accordingly, the insulating filmsobtained are those simply having the shrinkage factor, water absorption,ability of flattening and dielectric constant thereof falling within theranges achieved by the conventional techniques. On the other hand, ifthe value y exceeds 1.3, the heat-polymerization of the oligomer becomesdifficult and does not form any film, but results in the formation of arubbery substance. For this reason, the upper limit of y is defined tobe 1.3.

According to the conventional techniques, it has been believed that thehigher the value y, the lower the adhesion of the resulting film to thesurface of a substrate and that such siloxane oligomer cannotpractically be used. The ladder methylsiloxane is expressed by thechemical formula identical to that of the siloxane oligomer used in thepresent invention and the value y falls within the range defined in thepresent invention (the value y should be 1 to form a ladder structure),but it likewise suffers from problems of poor adhesion and highshrinkage and therefore, it is difficult to put it into practical use,as has already been discussed above in connection with the "BackgroundArt".

In the present invention, the problem of reduction in the adhesion dueto the use of the siloxane oligomer having a large y is solved by usingsiloxane oligomers comprising skeletons having random structures,limiting the molecular weight thereof and limiting the solvent tospecific ones. Thus, it would be believed that the selection of such arandom structure permits the incorporation of a large amount of Si--OHterminals which contribute to the adhesion into the oligomer structure,the resulting Si--O--Si network structure becomes sparse, whereby thefilm is softened and the ability of the film to absorb stresses isenhanced and accordingly, the adhesion of the resulting film isimproved. Although there has not yet been developed any appropriateparameter for defining the random structure, the conventional organicSOG is liable to have a regular structure even if the value y isincreased and accordingly, it is insufficient in the adhesion. If themolecular weight of the siloxane oligomer is less than 1500, it alsoundergoes a severe volume shrinkage during polymerization, an internalstress is easily generated and this becomes a cause of the formation ofcracks and peeling. Furthermore, if using a solvent having a boilingpoint of less than 120° C. , a problem of uneven coating arises due tothe difference in drying rate between portions on a plane and stressesare generated severely and this has a bad influence upon the adhesion.

In the present invention, the weight-average molecular weight of themethylsiloxane oligomer is limited to the range of from 1500 to 6000 forthe purpose of solving the foregoing problem of adhesion. Moreover, ifthe molecular weight is less than 1500, any continuous coating filmcannot be formed, while if it exceeds 6000, the viscosity of theresulting coating solution becomes too high and this becomes a cause ofthe generation of radial unevenness called striation. The weight-averagemolecular weight of the siloxane oligomer most preferably ranges from1500 to 3500.

A solvent mainly comprising an organic solvent having a boiling point ofnot less than 120° C. and not more than 200° C. is used as the solventfor dissolving the foregoing methylsiloxane oligomer. If the boilingpoint of the solvent is less than 120° C. , most of the solvent isevaporated due to the rotational motion during the coating operation andtherefore, the surface cannot be sufficiently flattened due to thefilling up effect of the coating solution. Moreover, a problem ofreduction in the adhesion arises due to the generation of stressesduring drying operations as has been described above. On the other hand,if the boiling point of the solvent exceeds 200° C. , the drying rate isconsiderably reduced. This leads to a decrease in the throughput,formation of defects during transportation of the substrates andproblems of foaming and residual carbon during heating steps arise.Therefore, such a solvent cannot be used in the present invention. Theboiling point of more preferably used solvents ranges from 130° to 160°C.

Incidentally, the coefficient of viscosity of the solvent greatlyaffects the ability of the coating solution to fill up fine grooves andthe uniformity of the coated film. Therefore, the solvent usedpreferably has a coefficient of viscosity, as determined at 25° C. , ofnot more than 2.0 cP. More specifically, if the coefficient of viscosityof the solvent is higher than 2.0 cP, the coating solutioninsufficiently runs into grooves of not more than 0.2 μm and there isobserved, during application of the coating solution, a considerableincrease in the frequency of the occurrence of so-called striation,i.e., unevenness in the film thickness in the form of radial stripedpattern which extends from the center of a substrate towards theperiphery thereof.

Examples of solvents which can satisfy the requirements of the presentinvention and accordingly can be used in the invention are ethyleneglycol monoethyl ether, ethylene glycol monoisopropyl ether, propyleneglycol monomethyl ether, ethylene glycol monoethyl ether acetate,diethylene glycol dimethyl ether, di-n-butyl ether, di-isobutyl ether,di-n-amyl ether, methyl n-amyl ketone, methyl isoamyl ketone, n-amylacetate, isoamyl acetate and n-hexyl acetate.

These solvents may be used alone, but may also be used in anycombination of at least two of them. Moreover, it is also possible toadd, to the solvent, other low boiling point solvents such as methanol,ethanol, isopropyl alcohol, acetone, methyl ethyl ketone, water andbutyl acetate in order to reduce the coefficient of viscosity and thecoating properties of the resulting coating solution. In this regard,however, if adding a solvent other than those having a boiling point ofnot less than 120° C. and not more than 200° C. , it is preferred thatthe volumetric rate thereof does not exceed 50% of the total volume ofthe solvent mixture. Incidentally, the foregoing solvents may of coursebe used for dissolving the siloxanes to prepare the coating solutionaccording to the second embodiment of the present invention.

If using the coating solution satisfying the foregoing requirements,there is observed a quite characteristic phenomenon which can be called"self-fluidization", i.e., the film once dried and solidified issoftened during heating, is again fluidized and the surface thereof isfurther flattened. The surface leveling due to the self-fluidizationtakes place at a temperature ranging from 150° to 200° C. , which islower than the temperature at which the methylsiloxane oligomer iscondensed and hardened. This phenomenon permits the leveling of aconsiderably wider area as compared with the conventional SOG.

The use of either or both of the coating solutions according to thesecond and third embodiments of the present invention permits theachievement of uniform flatness over the entire pattern on the substratesurface, complete filling up of fine grooves, the formation of a thickfilm sufficient for leveling the steps formed on the substrate surfaceand the formation of an insulating film which is free of water, has alow dielectric constant, is excellent in the insulating properties andis suitably used for producing a high speed interconnection, for thereasons discussed above.

The organic SOG coating solution having such characteristic propertiescan be prepared by the method for preparing a coating solution accordingto the fourth embodiment of the present invention. More specifically,the method makes use of a compound selected from the group consisting ofcompounds such as alkoxysilanes and alkylalkoxysilanes, in particular,tetraalkoxysilanes, methyltrialkoxysilanes and dimethyldialkoxysilanesor a mixture of at least two of them as a starting material and themethod comprises the steps of blending the starting materials in such amanner that the molar concentration of Si--CH₃ in the resulting blend isnot less than 80% and not more than 130% on the basis of the molarconcentration of Si present in the total starting materials, addingwater to the blend in an amount of 2 to 4 times the molar amount of theblend, heating the mixture at a temperature of not less than 40° C. andnot more than 80° C. in the presence of an organic carboxylic acid as acatalyst to thus polymerize the mixture, diluting the polymerizedproduct by addition of a solvent mainly comprising an organic compoundhaving a boiling point of not less than 120° C. and not more than 200°C. and then distilling the diluted solution under ordinary pressure or areduced pressure to thus distill off the water and alcohol asby-products of the polymerization reaction.

In this method, the tetraalkoxysilane generally used istetramethoxysilane (Si(OCH₃)₄) or tetraethoxysilane (Si(OC₂ H₅)₄); themethyltrialkoxysilane generally used is methyltrimethoxysilane (CH₃Si(OCH₃)₃) or methyltriethoxysilane (CH₃ Si(OC₂ H₅)₃); and thedimethyldialkoxysilane is dimethyldimethoxysilane ((CH₃)₂ Si(OCH₃)₂) ordimethyldiethoxysilane ((CH₃)₂ Si(OC₂ H₅)₂). At least one of thesestarting materials is blended in advance in such a manner that the molarconcentration of Si--CH₃ in the resulting blend is not less than 80% andnot more than 130% on the basis of the molar concentration of Si presentin the total starting materials. The range of the concentration is equalto the range of the value y when methylsiloxane oligomer is expressed bythe chemical formula: (CH₃)_(y) SiO₂₋(y/2). In other words, the value yin the chemical formula should be limited to not less than 0.8 and notmore than 1.3.

If methyltrimethoxysilane is, for instance, used as a starting material,the value, Si--CH₃ /total Si, of the silane per se is 100% whichcorresponds to y=1 and therefore, methyltrimethoxysilane can be usedalone. Moreover, if tetramethoxysilane and methyltrimethoxy-silane aremixed, the value y falling within the range: 0.8≦y<1.0 can be achievedby adjusting the mixing ratio r defined by Si(OCH₃)₄ !/ CH₃ Si(OCH₃)₃ !such that it falls within the range: 0<r≦0.25. If tetramethoxysilane anddimethyldimethoxysilane are mixed, the value y falling within the range:0.8≦y≦1.3 can be achieved by adjusting the mixing ratio r defined bySi(OCH₃)₄ !/ (CH₃)₂ Si(OCH₃)₂ ! such that it falls within the range:7/13≦r≦1.5. As has been discussed above, two or three kinds of startingmaterials may be used in combination.

If the molar concentration of Si--CH₃ included in the blend of startingmaterials or a single starting material is less than 80% of the molarconcentration of Si included in the whole starting material, the value yof the resulting methylsiloxane oligomer, when the latter is representedby the chemical formula: (CH₃)_(y) SiO₂₋(y/2), is less than 0.8 andtherefore, the resulting coating solution cannot show the desiredcharacteristic properties for the reasons discussed above. On the otherhand, if the molar concentration of Si--CH₃ included in the blend ofstarting materials or a single starting material exceeds 130% of themolar concentration of Si included in the whole starting material, thevalue y of the resulting methylsiloxane oligomer likewise exceeds 1.3and accordingly, any hardened film cannot be formed for the reasonsdiscussed above.

Water is then added to the ingredient thus prepared in an amount of 2 to4 times the molar amount of the latter and the condensation reactionthereof is initiated immediately after the addition of an organiccarboxylic acid such as formic acid, acetic acid or succinic acid andthus a polymer is formed. If the amount of water is less than 2 timesthe molar amount of the ingredient, the reaction rate is considerablylowered and the rate of the alkoxy groups remaining in the polymerincreases and correspondingly, this often leads to an increase in theamount of carbon remaining in the resulting film. On the other hand, ifthe amount of water exceeds 4 times the molar amount of the ingredient,not only the rate of production reaction is too high to control thereaction, but also the rate of free hydroxyl groups (Si--OH) in themethylsiloxane oligomer becomes too high and the resulting coatingsolution is insufficient in the storage stability.

The concentration of the organic carboxylic acid as a catalyst is notparticularly restricted since it does not affect the structure and stateof the product, but if the concentration thereof is extremely high, thereaction solution has a tendency to become acidic and this affects thestability of the resulting coating solution. Therefore, theconcentration thereof should be as low as possible and preferably rangesfrom about 1/1000 to 1/100 mole on the basis of the ingredient.Inorganic acids such as hydrochloric acid and phosphoric acid other thanorganic acids should not be used since they have an influence on metalspresent on a substrate to which the coating solution is applied.

After the addition of water, the components of the liquid mixture is notgenerally compatible with one another and therefore, the mixture mustvigorously be stirred using, for instance, a stirrer. Alcohols asby-products of the hydrolysis reaction are formed within several minutesto several hours and the hydrophilicity of the polymer formed increases.Accordingly, the components of the mixture are compatible with oneanother.

The reaction mixture may be diluted, in advance, by addition of asolvent such as alcohols prior to the polymerization reaction. Forinstance, the addition of methanol in an amount of 0.5 time the molaramount of the ingredient permits the reduction of heat generation at theinitial stage of the reaction, improvement of the stability of thereaction through improvement in the compatibility of the components andretardation of the polymerization reaction. Solvents added to thereaction mixture for this purpose are, for instance, methanol, ethanoland dioxane and used in an amount ranging from 0.2 to 3 times the molaramount of the ingredient.

To polymerize the methylsiloxane oligomer till the weight-averagemolecular weight of the resulting polymer reaches 1500 to 6000, theforegoing reaction mixture is heated at a temperature of not less than30° C. and not more than 80° C. In this respect, if the molarconcentration of Si--CH₃ included in the blend of the starting materialsor a single starting material relative to the molar concentration of Sipresent in the whole starting materials, i.e., the value y is relativelylow, the polymerization is preferably carried out at a low temperature,while if the value y is relatively high, the oligomer is preferablypolymerized at a relatively high temperature. If the heating temperatureis less than 30° C. , the polymerization rate is too low to obtain apolymer having a desired molecular weight. On the other hand, if theheating temperature exceeds 80° C., the control of the molecular weightof the resulting polymer becomes difficult since alcohols as by-productscause boiling and the polymerization reaction considerably rapidlyproceeds. In general, it is preferred to carry out the reaction at atemperature of about 50° C. while maintaining the reaction system, in asealed reactor, in a thermostatic chamber. The time required for thereaction varies depending on the reaction temperature used, but is notparticularly limited and it is sufficient to properly select thereaction time so that it falls within the range of from about 4 to 120hours while monitoring the molecular weight of the product formed.

Alcohols as by-products, a solvent when the solvent is added fordilution or the like, in addition to the water initially added as aningredient coexist in the polymerization product thus obtained. Theymust be removed, but if the polymerization product is distilled or driedwithout any pretreatment, the concentration of the methylsiloxaneoligomer is abruptly increased, the rate of polymerization acceleratedlyrises and this leads to the formation of a gel having a molecular weightof not less than several hundreds of thousands. For this reason, theremoval of the water, alcohols and solvent should be so designed thatthe concentration of the methylsiloxane oligomer is not increased. Tothis end, it is necessary to add, in advance, a main solvent used forthe dilution, i.e., a solvent mainly comprising an organic compoundhaving a boiling point of not less than 120° C. and not more than 200°C. to the polymerization product to dilute the product and to thendistill the diluted product under ordinary pressure or a reducedpressure. In this respect, it is important to appropriately select thedistillation temperature and pressure as conditions for the distillationso that the water, alcohols and solvent are distilled off, but the mainsolvent is not distilled off.

The same solvents used in the coating solution according to the thirdembodiment of the present invention can of course be used as such mainsolvents.

The methylsiloxane oligomer solution obtained after the removal of thewater, alcohols and solvent according to the foregoing method may beused as such or may be subjected to addition of a proper solvent andoptional filtration and ripening before practical use thereof as acoating solution.

The method for forming an insulating film for semiconductor devicesaccording to the fifth embodiment of the present invention which makesuse of the coating solution of the third embodiment of the presentinvention prepared according to the method of the fourth embodiment ofthe present invention and/or the coating solution of the secondembodiment of the present invention comprises the steps of applying thecoating solution according to the second and/or third embodiments of thepresent invention onto a distributing wire pattern formed on a siliconsubstrate and having step-like unevenness on the surface thereof, thendrying the coated solution, maintaining the dried coating solution at atemperature of not less than 150° C. and not more than 300° C. for notless than 30 seconds to thus fluidize it and then hardening it at atemperature of not less than 350° C. and not more than 450° C. in anitrogen gas atmosphere to form an insulating film. Thus, the presentinvention permits the production of a semiconductor device having aninsulating film, in particular, an interlayer insulating film excellentin film characteristic properties.

This method is roughly identical to the conventional method for forminga film of an organic SOG, but the present invention is characterized inthat the dried coating solution is maintained at a temperature of notless than 150° C. and not more than 300° C. for not less than 30seconds, in the light of the fact that the SOG of the present inventionhas a self-fluidization temperature of not less than 150° C. and notmore than 300° C. , to thus complete the surface-leveling while makinguse of the self-fluidizing ability of the SOG. More specifically, a filmobtained by applying the coating solution and then drying is againfluidized within the foregoing temperature range to thus ensure flatnessof the surface over a wide area. The subsequent steps are no more thanthe usual ones called SOG curing steps.

EXAMPLES

The present invention will hereinafter be described in morespecifically.

Example 1

A siloxane oligomer contained in a commercially available organic SOGwas inspected for the rates of the foregoing structural units (a), (b),(c) and (d) present therein and the contents of organic substituentspresent therein. In this Example, two kinds of organic SOG's, i.e.,Sample A (SF 1014 available from Sumitomo Chemical Co., Ltd.) and SampleB (Type 12000T available from Tokyo Ohka Kogyo Co., Ltd.) were analyzed.

Each organic SOG (Sample A or B; 1.5 ml each) and tris(acetylacetonato)Cr(III) (about 40 mg) were added to and dissolved in 1.5 ml of deuteroacetone to give a uniform solution. The solution was introduced into anNMR sample tube of Teflon having an inner diameter of 10 mm andsubjected to ²⁹ Si-NMR measurement using a Fourier transform NMRspectrometer (GX 270 available from JEOL Ltd.). The observed centralfrequency was 53.67 MHz, the observed frequency range was 16 kHz, thedata points were 16k or 32k, the integration number was 10000-45000 andtetramethylsilane was used as the internal standard.

An example of the resulting ²⁹ Si-NMR spectrograms is shown in FIG. 1.The relative ratios of the foregoing A₀, A₁, A₂ and A₃ were determinedon the basis of the area of each signal shown in FIG. 1. In thisrespect, the area of each peak shown in FIG. 1 is in proportion to thenumber of Si atoms present in each corresponding structural unit. Incase of structural units (a) and (c), the sum of the areas of aplurality of peaks shown in FIG. 1 is in proportion to the number of Siatoms present in each structural unit.

In addition, the contents of the organic substituents defined by theforegoing Formula 3! were calculated. The results thus obtained aresummarized in the following Table 1.

In this Example, the substituent R is a methyl group.

As has been described above, the rate of each structural unit (it hasbeen impossible to determine the same by the conventional methods)present in organic siloxanes can be determined by analyzing the contentsof organic substituents present in the organic siloxanes by the ²⁹Si-NMR spectroscopic measurement using the evaluation method accordingto the first embodiment of the present invention. For instance, theevaluation method permits easy determination of the rates of thestructural units (a), (b), (c) and (d) present in an organic SOG and thecontents of organic substituents present therein.

                                      TABLE 1                                     __________________________________________________________________________    Rates of Structural Units and Contents of Organic Substituents                Rates of Structural Units                                                     Rate (%) of the number of Si atoms present in each                            structural unit (a), (b), (c) or (d) to the total                             number of Si atoms present in siloxane                                             (d)    (b)     (a)     (c)                                                     ##STR8##                                                                             ##STR9##                                                                              ##STR10##                                                                             ##STR11##                                                                            Content of Organic Substituents                                               Defined by Formula  3!                    __________________________________________________________________________    Sample A                                                                           0      11      40      49      62                                        Sample B                                                                           0       0      46      54      46                                        __________________________________________________________________________

Example 2

Methyltrimethoxysilane and tetramethoxysilane were dissolved in methanolin a rate listed in Table 2, followed by adding water in a rate listedin Table 1 and 0.002 mole of formic acid to the resulting solution andthen carrying out a polymerization reaction at 30° to 60° C. for 24hours with stirring. To the reaction product, there was added 650 ml ofa 1:1 mixture of benzene and ethylene glycol monoethyl ether, followedby distillation under a reduced pressure to remove the excess methanoland water to give a coating solution having a solid content of about 20%by weight. The weight-average molecular weight of the siloxane oligomerincluded in the coating solution was determined by the gel permeationchromatography and was found to be about 3,000 which corresponded to adegree of polymerization ranging from 40 to 50.

The coating solution was applied onto a silicon wafer having a diameterof 6 inches by spin coating at a rotational frequency of 3,000 rpm, theresulting layer of the solution was baked at 150° C., 200° C. or 250° C.for 60 seconds and then heated at 400° C. for 30 minutes in a nitrogengas stream to give a coating film.

The resulting film was inspected for the shrinkage factor, dielectricconstant and water absorption. The results thus obtained are shown inthe following Table 2 and FIG. 2 together with the value X defined byFormula 2!.

In this respect, the shrinkage factor was evaluated by forming coatingfilms different, in thickness, from one another on washed semiconductorsubstrates while controlling the rotational frequency and thencalculating the factor according to the following Formula 5!:

    Shrinkage Factor (%)={(t.sub.b -t.sub.a)/t.sub.b }×100 5!

wherein t_(a) represents the thickness of the film after the hardeningtreatment and t_(b) represents the thickness of the film after theprebaking treatment.

The dielectric constant was determined by forming an Al film on thewhole surface of a washed semiconductor substrate through sputtering,then forming a coating film having a thickness of about 300 nm whilecontrolling the rotational frequency according to the foregoing method,subjecting the film to prebaking and curing treatments, vapor-depositingan Al electrode of about 3 mm square through a metal mask, etching theedge portion of the film with diluted hydrofluoric acid, measuring theelectrostatic capacity between the lower whole Al surface and thevapordeposited Al film and calculating the dielectric constant on thebasis of the electrode surface area and the film thickness.

Moreover, the water absorption, i.e., the amount of water included inthe film was determined by allowing, to stand, a film after thecompletion of the hardening treatment for 24 hours in a clean room andthen measuring the amount of water generated till the temperaturereached 400° C. using an electrolytic cell type moisture meter (MEA(Moisture Evaluation Analyzer) available from duPont de Nemours & Co.).

As seen from Table 2 and FIG. 2, there is a distinct relation betweenthe value X and the film properties and it has also been found that whenX≧80%, an excellent film can be obtained, whose shrinkage factor,dielectric constant and water absorption are low.

                                      TABLE 2                                     __________________________________________________________________________                             Reaction                                                                             X Defined   Specific                                                                            Water                           Methyltrimethoxy-                                                                      Tetramethoxy-                                                                        Water                                                                              Temperature                                                                          by Formula                                                                          Shrinkage                                                                           Inductive                                                                           Absorption                  No. silane (mole)                                                                          silane (mole)                                                                        (mole)                                                                             (°C.)                                                                          2!   Factor (%)                                                                          Capacity (-)                                                                        (wt %) Remarks              __________________________________________________________________________    1   0.0      1.0    0.5  30     0     10.0  14.0  6.6    Comparative          2   0.1      0.9    0.5  30     10    9.0   12.0  5.0    Examples             3   0.2      0.8    1.0  30     20    8.0   9.5   3.9                         4   0.3      0.7    1.0  30     30    7.2   6.2   2.9                         5   0.4      0.6    1.5  50     40    6.0   5.3   1.6                         6   0.5      0.5    2.0  50     50    5.8   4.4   0.2                         7   0.6      0.4    2.0  50     60    4.3   4.1   0.1                         8   0.7      0.3    2.0  50     70    3.2   3.8   0.0                         9   0.8      0.2    2.0  80     80    0.8   3.5   0.0    Present              10  0.9      0.1    2.0  80     90    0.0   3.2   0.0    Invention            11  1.0      0.0    2.0  80     100   0.0   3.0   0.0                         __________________________________________________________________________

Example 3

First of all, a coating solution of the present invention for formingSOG films was prepared according to the following procedures accordingto the method of the fourth embodiment of the present invention. In thepreparation, the mixing ratios of starting materials, the conditions forsynthesis and the typical film properties are summarized in thefollowing Tables 3 and 4. Table 3 shows three kinds of startingmaterials which are variously combined, while Table 4 shows dataobtained when a variety of conditions for synthesis are variouslychanged. Data practically determined are also listed in Tables 3 and 4.The details of the methods for determination will be described below.Physical properties of the film determined in this Example are the sameas those listed in Tables 3 and 4. The films beyond the scope of thepresent invention are comparative examples and specified by annexing anasterisk (*) to the front of each corresponding sample number.

Synthesis of Coating Solution

Tetramethoxysilane, methyltrimethoxysilane and dimethyldimethoxysilane(the purity of these compounds being not less than 99%) were admixedtogether in mixing ratios specified in Table 3 and 4, followed by addingwater to each mixture in a rate listed in Table 3 or 4, further adding a1N formic acid aqueous solution in an amount of 0.002 mole as expressedin terms of formic acid, stirring the mixture to give a uniformsolution, closely sealing the container including the mixture, immersingthe container in a thermostatic water bath maintained at a temperaturespecificed in Table 3 or 4 and polymerizing the mixture by maintainingit at that temperature for a time listed in Table 3 or 4. Methyl n-amylketone (2-heptanone; boiling point: 151° C.) was added to thepolymerized product as a solvent, followed by distilling the mixture at50° C. and 50 Torr using a rotary evaporator to remove the excessmethanol and water. Thereafter, the mixture was further diluted withmethyl n-amyl ketone (2-heptanone) to give a coating solution having asolid content of 20% by weight. The weight-average molecular weight ofthe siloxane oligomer included in the coating solution was determined bythe gel permeation chromatography and the results were also listed inTable 4. It is clear that all of the coating solutions synthesized inExamples shown in Table 4 satisfy the requirements for the coatingsolution according to the third embodiment of the present invention,except for the irregularity of the Si--O--Si network since there has notbeen developed any method capable of determining the irregularity.However, it is self-evident that the siloxane oligomers do not have aregular structure such as a ladder structure while taking intoconsideration the fact that the shrinkage factor as will be detailedbelow is very small.

Each coating solution was applied onto a silicon wafer having a diameterof 6 inches by spin coating at a rotational frequency of 3,000 rpm, theresulting layer of the solution was baked at 150° C., 200° C. or 250° C.for 60 seconds and then heated at 400° C. for 30 minutes in a nitrogengas stream to give a coated film.

The resulting film was inspected for the shrinkage factor, dielectricconstant and water absorption. The results thus obtained are shown inthe following Table 3 together with the value y in the followingchemical formula 1:

    (CH.sub.3).sub.y SiO.sub.2-(y/2)                           (chemical formula 1)

The shrinkage factor, dielectric constant and water absorption of thefilm were determined and evaluated in the same manner used in Example 2.

As seen from Tables 3 and 4, there is a distinct relation between thevalue y and the film properties and it has also been found that when0.8≦y≦1.3, an excellent film can be obtained, whose shrinkage factor anddielectric constant are small and whose water content is low.

Then the method for forming an insulating film according to the fifthembodiment of the present invention will be explained below withreference to the attached drawings.

FIG. 3 is a partially sectional view showing the processes for formingan insulating film according to the present invention. In the processshown in FIG. 3A, a distributing wire layer having a thickness of 1.2 μmwas formed on a semiconductor substrate 1 which has been subjected to adesired treatment, then the layer was subjected to patterning to form aline-and-space distributing wire pattern 2 comprising distributing wires2a, 2b and 2c having a width of the wire of 1 μm (distance between thewires 2a and 2b=distance between the wires 2b and 2c=1 μm) and aline-and-space distributing wire pattern 3 comprising distributing wires3a, 3b and 3c having a width of the wire of 0.5 μm (distance between thewires 2a and 2b=distance between the wires 2b and 2c=0.5 μm). Thedistance between the distributing wire patterns 2 and 3 was set at 3 μm.This process was accompanied by the formation of steps between thesemiconductor substrate 1 and the distributing wire patterns 2 and 3.

In the subsequent process shown in FIG. 3B, an SiO₂ layer 4 wasdeposited on the whole surface of the semiconductor substrate 1 and thedistributing wire patterns 2 and 3 obtained in the process shown in FIG.3A in a thickness of 300 nm by the plasma CVD technique usingtetraethoxysilane (TEOS). This CVD oxide film 4 is excellent in the stepcoverage, but could not fill up the grooves between the distributingwires since the film was formed along the shape (steps) of the surfaceof the substrate.

In the next process shown in FIG. 3C, each coating solution prepared inthe foregoing method and shown in Table 3 or 4 as an ingredient for aninsulating film was applied onto the oxide film 4 in a thickness rangingfrom 0.7 or 1.1 μm by the spin coating technique to form an insulatingfilm 5 and the resulting layer of the solution was pre-baked at 80° C.,150° C. or 230° C. for 60 seconds in a nitrogen gas atmosphere.Thereafter, the pre-baked layer was cured (hardened) by heating it at400° C. for 30 minutes in a nitrogen gas stream to give an insulatingfilm 5. Thus, a semiconductor device 6 of the present invention wasproduced. The cross section of the insulating film 5 of the resultingsemiconductor device 6 was observed. In the evaluation of the flatness,the tendency of the insulating film was specifically examined using themeasure (DOP) for the flatness shown in FIG. 4. Incidentally, themeasure for the flatness, i.e., DOP (%) was determined according to thefollowing equation:

    DOP(%)={ 1-(θ/90)(d.sub.0 /d.sub.m)}×100

wherein θ represents the slope of the step of the insulating film 8originated from the distributing wire 7 as shown in FIG. 2; d₀represents the difference of altitude; and d_(m) represents thethickness of the distributing wire 7.

The results of the measurement of the flatness are listed in Tables 3and 4.

It is found that excellent flatness can be ensured through the use ofeither of the SOG's according to the present invention.

                                      TABLE 3                                     __________________________________________________________________________              Methyltri-                                                                         Dimethyl-        Value y                                          Tetramethoxy-                                                                        methoxy-                                                                           dimethoxy-       in   Shrinkage Flatness                                                                           Water                     Ex.                                                                              silane silane                                                                             silane                                                                              Water                                                                              Reaction                                                                            Chemical                                                                           Factor                                                                             Dielectric                                                                         DOP  Absorption                No.                                                                              (mole) (mole)                                                                             (mole)                                                                              (mole)                                                                             Condition                                                                           Formula 1                                                                          (%)  Constant                                                                           (%)  (wt                                                                                 Remarks             __________________________________________________________________________    *1 1.0    0.0  0.0   3    50° C., 24 h                                                                 0.0  25   5.4  0.50 6.6   formation                                                                     of cracks            2 0.3    0.7  0.0   3    50° C., 24 h                                                                 0.7  6    4.2  0.65 1.8                        3 0.2    0.8  0.0   3    50° C., 24 h                                                                 0.8  3    3.5  0.90 0.2                        4 0.1    0.9  0.0   3    50° C., 24 h                                                                 0.9  1    3.3  0.90 <0.1                       5 0.0    1.0  0.0   3    50° C., 24 h                                                                 1.0  0    3.0  >0.90                                                                              <0.1                       6 0.1    0.8  0.1   3    50° C., 24 h                                                                 1.0  0    3.0  >0.90                                                                              <0.1                       7 0.5    0.0  0.5   3    50° C., 24 h                                                                 1.0  0    3.0  >0.90                                                                              <0.1                       8 0.0    0.9  0.1   3    50° C., 24 h                                                                 1.1  0    2.9  >0.90                                                                              <0.1                       9 0.1    0.7  0.2   3    50° C., 24 h                                                                 1.1  0    2.9  >0.90                                                                              <0.1                      10 0.0    0.8  0.2   3    50° C., 24 h                                                                 1.2  0    2.9  >0.90                                                                              <0.1                      11 0.0    0.74 0.28  3    50° C., 24 h                                                                 1.3  0    2.8  >0.90                                                                              <0.1                      12 0.2    0.3  0.5   3    50° C., 24 h                                                                 1.3  0    2.7  >0.90                                                                              <0.1                      *13                                                                              0.0    0.6  0.4   3    50° C., 24 h                                                                 1.4  --   --   --   --    film is                                                                       not                                                                           formed              *14                                                                              0.3    0.0  0.7   3    50° C., 24 h                                                                 1.4  --   --   --   --    film is                                                                       not                                                                           formed              __________________________________________________________________________

                                      TABLE 3                                     __________________________________________________________________________              Methyltri-                                                                         Dimethyl-        Average                                          Tetramethoxy-                                                                        methoxy-                                                                           dimethoxy-       molecular                                                                          Shrinkage Flatness                                                                           Water                     Ex.                                                                              silane silane                                                                             silane                                                                              Water                                                                              Reaction                                                                            weight of                                                                          Factor                                                                             Dielectric                                                                         DOP  Absorption                No.                                                                              (mole) (mole)                                                                             (mole)                                                                              (mole)                                                                             Condition                                                                           Oligomer                                                                           (%)  Constant                                                                           (%)  (wt                                                                                 Remarks             __________________________________________________________________________    *15                                                                              0.0    1.0  0.0   1    50° C., 24 h                                                                 1200 7    3.3  0.70 <0.1  uneven in                                                                     film                                                                          thickness           16 0.0    1.0  0.0   2    50° C., 24 h                                                                 1900 1    3.1  >0.90                                                                              <0.1                      17 0.0    1.0  0.0   3    50° C., 24 h                                                                 2500 0    2.9  >0.90                                                                              <0.1                      18 0.0    1.0  0.0   4    50° C., 24 h                                                                 2800 0    2.9  >0.90                                                                              <0.1                      *19                                                                              0.0    1.0  0.0   5    50° C., 24 h                                                                 9000 0    2.9  >0.90                                                                              <0.1  uneven in                                                                     film                                                                          thickness           *20                                                                              0.0    1.0  0.0   3    30° C., 24 h                                                                  700 10   3.6  0.70 <0.1  uneven in                                                                     film                                                                          thickness           21 0.0    1.0  0.0   3    40° C., 24 h                                                                 1600 0    3.0  >0.90                                                                              <0.1                      22 0.0    1.0  0.0   3    60° C., 24 h                                                                 2800 0    3.0  >0.90                                                                              <0.1                      23 0.0    1.0  0.0   3    70° C., 24 h                                                                 5200 0    3.0  >0.90                                                                              <0.1                      24 0.0    1.0  0.0   3    60° C., 24 h                                                                 4000 0    3.0  >0.90                                                                              <0.1                      __________________________________________________________________________

INDUSTRIAL APPLICABILITY

As has been described above in detail, the evaluation method accordingto the present invention permits, in the analysis of the contents oforganic substituents of organic siloxanes, the determination of the rateof each structural unit (it has been impossible to determine the same bythe conventional methods) present in the organic siloxanes and thedetermination of the contents of the organic substituents present in theorganic siloxanes.

Therefore, the present invention can be used for evaluating theorganicity of the siloxanes present in a solution containing the samewhich is used for forming, for instance, an insulating film forsemiconductor devices, in particular, an interlayer insulating film forLSI multilevel interconnections and the evaluation method of the presentinvention permits the prediction of the film properties of theinsulating film such as the resistance to chemicals and the waterresistance. Moreover, the present invention has such an effect that theaccurate quality control of SOG's used for forming an insulating filmcan be ensured during the production of the SOG's.

In addition, the use of the coating solution containing the siloxanes ofthe present invention, in particular, methylsiloxane oligomer permitsthe formation of an insulating film for semiconductor devices such as aninterlayer insulating film for LSI multilevel interconnections havingexcellent film properties.

In other words, if using the coating solution and the method for formingan insulating film, which makes use of the coating solution, accordingto the present invention, an insulating film having excellent filmproperties can be prepared, i.e., they permit the achievement of uniformflatness over the whole pattern on the substrate and complete filling upof fine grooves, the resulting insulating film exhibits excellentresistance to cracks, they can form a thick film sufficient foreliminating the steps on the substrate, i.e., leveling the substratesurface and they permit the formation of an insulating film free ofmoisture, having a low dielectric constant and effective for use in highspeed interconnections, in particular, an interlayer insulating film forsemiconductor devices.

In addition, the method for preparing the coating solution of thepresent invention permits stable production of a coating solutionshowing the foregoing effects with certainty.

Furthermore, the method for producing a semiconductor device accordingto the present invention likewise permits stable production ofsemiconductor devices provided with interlayer insulating filmsexcellent in the foregoing film properties, with certainty.

What is claimed is:
 1. A method for evaluating an organicity ofsiloxanes in coating solutions for forming an insulating film used inproduction of semiconductor devices, the method comprising the stepsof:providing a sample of siloxanes to be analyzed; introducing thesample into an NMR spectrometer; integrating ²⁹ Si-NMR spectral signalsto determine numbers of silicon atoms in the siloxanes bonded to three,two, one and zero organic group; and evaluating the organicity, whereinthe step of evaluating comprises calculating ratios of the numbers ofsilicon atoms in the siloxanes bonded to three, two, one and zeroorganic group.
 2. The method according to claim 1, wherein the siloxanesare represented by a general formula:

    (SiR.sub.3 O.sub.1/2).sub.k (SiR.sub.2 O.sub.2/2).sub.l (SiRO.sub.3/2).sub.m (SiO.sub.4/2).sub.n

where each of k, l, m and n is an integer ranging from 0 to 1000, atleast one of k, l and m is greater than zero, R may be the same ordifferent and represents at least one organic group selected from thegroup consisting of a saturated hydrocarbon group, an unsaturatedhydrocarbon group, a phenyl group and a substituted phenyl group; andwherein said step of evaluating comprises calculating a ratio of m to(k+l+m+n).
 3. The method according to claim 2, wherein said organicgroup is a methyl group.
 4. The method according to claim 1, wherein thesiloxanes are represented by a general formula:

    (SiR.sub.3 O .sub.1/2).sub.k (SiR.sub.2 O.sub.2/2).sub.l (SiRO.sub.3/2).sub.m (SiO.sub.4/2).sub.n

where each of k, l, m and n is an integer ranging from 0 to 1000, atleast one of k, l and m is greater than zero, R may be the same ordifferent and represents at least one organic group selected from thegroup consisting of a saturated hydrocarbon group, an unsaturatedhydrocarbon group, a phenyl group and a substituted phenyl group; andwherein said step of evaluating comprises calculating a ratio of(3k+21+m) to (k+l+m+n).
 5. The method according to claim 4, wherein saidorganic group is an alkyl group.
 6. The method according to claim 5,wherein said organic group is a methyl group.
 7. A method for forming aninsulating film comprising the steps of:providing a substrate of asemiconductor device, a surface of the substrate having stepped, unevenplanes; coating a coating solution on the surface of the substrate toform a coated film; fluidizing the coated film at a temperature of notless than 150° C. and not more than 300° C. to flatten a surface of thecoated film; and curing the fluidized coated film to form the insulatingfilm; wherein the coating solution comprises a solvent and siloxanesdissolved in the solvent, the siloxanes represented by a generalformula:

    (SiR.sub.3 O.sub.1/2).sub.k (SiR.sub.2 O.sub.2/2).sub.l (SiRO.sub.3/2).sub.m (SiO.sub.4/2).sub.n

where each of k, l, m and n is an integer ranging from 0 to 1000, atleast one of k, l and m is greater than zero, R may be the same ordifferent and represents at least one organic group selected from thegroup consisting of a saturated hydrocarbon group, an unsaturatedhydrocarbon group, a phenyl group and a substituted phenyl group, and aratio of (3k+21+m) to (k+l+m+n) is not less than 0.8 and not more than1.3.
 8. A method for forming an insulating film for a semiconductordevice comprising the steps of:providing a substrate of thesemiconductor device; coating a coating solution on a surface of thesubstrate to form a coated film; prebaking the coated film at atemperature of not less than 150° C. and not more than 300° C. to form aprebaked coated film; and curing the prebaked coated film to form theinsulating film; wherein the coating solution comprises a solvent andsiloxanes dissolved in the solvent, the siloxanes represented by ageneral formula:

    (SiR.sub.3 O.sub.1/2).sub.k (SiR.sub.2 O.sub.2/2).sub.l (SiRO.sub.3/2) (SiO.sub.4/2).sub.n

where each of k, l, m and n is an integer ranging from 0 to 1000, atleast one of k, l and m is greater than zero, R may be the same ordifferent and represents at least one organic group selected from thegroup consisting of a saturated hydrocarbon group, an unsaturatedhydrocarbon group, a phenyl group and a substituted phenyl group, and aratio of (3k+21+m) to (k+l+m+n) is not less than 0.8 and not more than1.3; and a shrinkage factor defined by the formula (t_(b) -t_(a))/t_(b)×100 is not more than 3%, where t_(a) is a thickness of the insulatingfilm and t_(b) is a thickness of the coated film before the step ofcuring.
 9. The method according to claim 7, wherein said siloxanes arerandom structured siloxanes.
 10. The method according to claim 7,wherein R of the siloxanes represents an alkyl group.
 11. The methodaccording to claim 10, wherein R of the siloxanes represents a methylgroup.
 12. The method according to claim 7, wherein said step offluidizing is performed in a nitrogen ambient.
 13. The method accordingto claim 7, wherein said step of fluidizing is performed at atemperature ranging from 150° C. to 200° C.
 14. The method according toclaim 7, wherein said solvent of the coating solution includes anorganic compound having a boiling point of not less than 120° C. and notmore than 200° C.
 15. The method according to claim 14, wherein saidboiling point of the organic compound ranges from 130° C. to 160° C. 16.The method according to claim 7, wherein a weight average molecularweight of the siloxanes in the coating solution is between 1500 and6000.
 17. The method according to claim 7, wherein a shrinkage factordefined by the formula (t_(b) -t_(a))/t_(b) ×100 is not more than 3%,where t_(a) is a thickness of the insulating film and t_(b) is athickness of the coated film before the step of curing.
 18. The methodaccording to claim 17, wherein said step of curing is performed at atemperature of not less than 350° C. and not more than 450° C.
 19. Themethod according to claim 17, wherein said step of curing is performedin a nitrogen ambient.
 20. The method according to claim 17, wherein Rof the siloxanes represents an alkyl group.
 21. The method according toclaim 17, wherein R of the siloxanes represents a methyl group.
 22. Themethod according to claim 17, wherein said step of fluidizing isperformed at a temperature ranging from 150° C. to 200° C.
 23. Themethod according to claim 7, wherein k is substantially equal to zero.24. The method according to claim 7, wherein a ratio of m to (k+l+m+n)is less than one.
 25. The method according to claim 8, wherein saidsiloxanes are random structured siloxanes.
 26. The method according toclaim 8, wherein said step of curing is performed at a temperature ofnot less than 350° C. and not more than 450° C.
 27. The method accordingto claim 8, wherein a weight average molecular weight of the siloxanesin the coating solution is between 1500 and
 6000. 28. The methodaccording to claim 8, wherein said step of curing is performed in anitrogen ambient.
 29. The method according to claim 8, wherein R of thesiloxanes represents an alkyl group.
 30. The method according to claim29, wherein R of the siloxanes represents a methyl group.
 31. The methodaccording to claim 8, wherein k is substantially equal to zero.
 32. Themethod according to claim 8, wherein a ratio of m to (k+l+m+n) is lessthan one.